UBC Theses and Dissertations
Masking on the high-frequency side of a masking tone : effects on masked threshold of selectively masking low-frequency combination tones of different types formed by signal and masker Krammer, Franz Georg
When signals are presented on the immediate high-frequency side of a pure-tone masker, it is not the signal, but rather combination tones, that are detected at masked threshold (Greenwood, 1971b. At low to moderate masker intensities, the detected combination tone is 2f1 minus f2, where f1 is the masker frequency and is the signal frequency. At higher masker levels, the combination tone f2-f1 becomes large enough to play a role. To investigate this role, the combination tones f2-f1 and 2f1-f2 were selectively masked in different low-frequency regions, to identify their effects. As has been known, the notch region on the high side of the pure-tone masking pattern creates a secondary peak, which shifts upward in frequency and height as masker intensity is raised. Results indicate that the frequency location of this secondary peak has an upper limit at 1.85f1, and that the secondary peak marks the beginning of signal-determined masked thresholds. At masker levels sufficient to shift this secondary peak upward, beyond 1.5 times the masker frequency (f1), both 2f1-f2 (or C1) and f2-f1 (or Dl) are deleted with about equal likelihood when signals are in the higher-frequency part of the notch region, at frequencies between l.5f1 and the secondary peak,, That is, either C1 or D1, or both, may be detected since their intensities become quite similar at higher levels, as supported by more direct estimates (Greenwood, 1971b, 1972a,b,c; Hall, 1971, 1972a,b).